Addressing someone you don't know as "Mr." or "Ms." is, to me, the only polite option. This is whether in writing or in person.
This assumes one (or more) criteria:
- The other person is a stranger to you;
- You are talking to someone in a business or service setting, particularly when, but not limited to when the other person is your customer, though I also tend to call people doing work for me "Mr." as well;
- The other person is older than you are (especially in this case), or of 'a certain age'. As for what age that is, I'm often stumped, though I tend to default to anyone above ~age 30.
For someone to accuse people who want to be called "Mr." as 'uptight' or to be told to 'get-over-it-man' as one often hears or reads, is ignorant in the extreme. Until something better is invented, a title conveys respect. Calling someone by their first name conveys, at best, familiarity--as between friends. At worst, it's a show of uninvited, slimy disrespect. It often comes across as a sneering: "Nyeah...you're nuthin' special, and I'll just make sure you know it--BOB."
I read somewhere a comment on this topic in which the young commenter felt that titles were unnecessary and archaic because "...we're all the same level...." Whether that's true or not, addressing someone by an admittedly more formal "Ms." need have nothing to do with hierarchy. It has everything to do with showing respect for the other person, and with giving her/him some psychological/social 'space', if you will. I doubt that those who want everyone to be laid-back and informal would be so gung-ho if a stranger or sales clerk physically came within inches of his/her face when they met or interacted? I didn't think so.
Calling someone by their first name before you're invited to is similar. It’s grabbing something that isn't yours to take. Just because most of us, by now, have been forced to "get used to it" doesn't mean its any less disrespectful. And just because virtually no one acknowledges anyone with "Mr." or "Ms." anymore, doesn't make it right.
~~[Post Scripts: In my argument above, I've deliberately defaulted to "Ms." for women and left out "Mrs." and "Miss" because, after much thought, I decided long ago that for me "Ms." is the most respectful of women since it's 'non-marital', as it were. Whether I'm right or not is totally open to debate. I know some women who detest one or more of all the three forms of address.
I also totally 'get' that there are many social situations where being on a first name basis right off the hop is completely fine--and expected. We all evaluate each new social situation in which we find ourselves. Calling new baseball teammates or your in-laws' nephew "Mr. StuffandSuch" would obviously sound just plain dumb.
I will also add in my defence, if I need to, that although I may come across as rigid, I actually came from a place and culture that, while quite conservative in almost every other way, encouraged even children to call adults by their first names. (Go figure.) In a very specific context like this, it was normal, expected and therefore acceptable.]